This invention is directed to methods for the improvement of petroleum residual materials. More particularly, means for the reduction of viscosity in residual petroleum fractions are disclosed which employ the grafting of olefins thereto.
The production of hydrocarbons from petroleum feedstocks generally results in the concomitant production of residuals. A residual in the present context is that portion of a petroleum feedstock which remains as a bottoms product after the distillation or removal of low and moderate boiling hydrocarbon fractions therefrom. Those skilled in the art will understand that such residuals are composed of complex pluralities of generally large hydrocarbon molecules, most of which are aromatic in character. Residuals are known to be extremely viscous; their economic utility is limited in part by this viscosity. Accordingly, methods for the reduction of viscosity in petroleum residuals are desired.
Heretofor, viscosity reduction in petroleum residuals has been accomplished through thermal visbreaking. Thus, residual petroleum fractions have been heated to temperatures upwards of 350.degree. C. for a period of time on the order of about 10 minutes. This heat treatment causes thermal "cracking" to occur. Such cracking, which is believed to comprise a diminution in the molecular weight of individual molecules comprising components of the residual, leads to a reduction in viscosity due to a reduction in component molecular weight. Thermal visbreaking has several serious shortcomings however. Accordingly, it known that the heating of residuals for too long a time or at too high a temperature results in their becoming incompatible with other petroleum species to the end that blending into useful hydrocarbon blends is rendered difficult. While the exact mechanism of the effect is not presently understood, it is known that stringently heat treated residuals will form sediment when blended with the lighter petroleum feedstocks; such sedimentation is highly undesirable.
At the same time, thermal visbreaking is expensive in terms of energy requirements; processes involving lower temperatures are to be desired. Accordingly, it has long been desired to provide methods for the lowering of viscosity of residuals, which methods may be undertaken at lower temperatures and which are not likely to lead to the formation of products prone to sedimentation.
It has been known to graft olefinic moieties onto coal in an attempt to improve liquifaction characteristics of coal. See in this regard; "Development of Clean, `Liquid` Coal Advanced," Combustion, Vol. 48 (10), pp. 34-37 (1977); U.S. Pat. No. 4,033,852-Horowitz et. al.; and U.S. Pat. No. 4,263,123-Ebert et. al. The improvement of petroleum residuals through chemical visbreaking in accordance with the present invention has not, however, been disclosed or suggested.